CppCompileAction must return false from inputsKnown for .d pruning

This is necessary (but not sufficient) for the action cache to work
correctly. Consider the following sequence of events:
1. action is executed
2. .d pruning is performed
3. action cache writes entry with post-pruning inputs list
4. action gets regenerated (e.g., due to server restart)
5. the action cache calls inputsKnown(), which returns true
6. action cache checks entry from step 3 against pre-pruning inputs list,
   which results in a cache miss

The action cache needs to know that the current list is not the final list,
so inputsKnown() in step 5 must return false if .d pruning is enabled.

This is a step towards resolving #2490.

--
PiperOrigin-RevId: 147738367
MOS_MIGRATED_REVID=147738367

1 files changed, 3 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
index 3f8437087f..7f433726c6 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
@@ -334,9 +334,11 @@ public class CppCompileAction extends AbstractAction
     // the inputs are as declared, hence known, and remain so.
     this.shouldScanIncludes = shouldScanIncludes;
     this.shouldPruneModules = shouldPruneModules;
+    // We can only prune modules if include scanning is enabled.
+    Preconditions.checkArgument(!shouldPruneModules || shouldScanIncludes, this);
     this.usePic = usePic;
     this.useHeaderModules = useHeaderModules;
-    this.inputsKnown = !shouldScanIncludes;
+    this.inputsKnown = !shouldScanIncludes && !cppSemantics.needsDotdInputPruning();
     this.cppCompileCommandLine =
         new CppCompileCommandLine(
             sourceFile, dotdFile, copts, coptsFilter, features, variables, actionName);